Various mechanisms are used in a hydraulic device, and a swash pump using a swash plate is a typical device. The swash pump is analogous to a slider-crank mechanism and mechanically constructed to convert a linear motion into a rotary motion or vice versa.
The slider-crank mechanism may be used in various constructions and classified, but basically the slider-crank mechanism is a device that converts the rotary motion of a crank into the linear motion of a slider.
When the rotary motion of the crank is converted into the linear motion of the slider, a motion displacement/a speed/an acceleration of a linear motion part accompany a sinusoid motion according to rotation amount .theta. of the crank. And when such slider-crank mechanism is used to operate a hydraulic system as a pump and the like, the ripple in output flow and pressure is known to result.
The hydraulic system connected to such a motion conversion device may comprise a pump for generating power, or an actuator actually working like a cylinder or a motor, a control valve for controlling the actuator, or an accessary mechanism playing a supplementary role and the like. Positive displacement pumps such as vane, gear and plunger type pumps are generally selected as the desired hydraulic system because of their ability to generate a high discharge pressure. A screw pump may be used in case of a large capacity or high viscosity.
However, a hydraulic head pressure generated by a hydraulic pump or a hydraulic motor and the like is also known to cause a ripple in the fluid being transported due to the construction or operational characteristics of the pump itself. For example, the hydraulic head pressure of a positive displacement piston operated pump is known to vary widely corresponding to the stroke of the pump piston displacing the fluid, causing ripple in the discharge fluid stream and irregular operation of the actuator in an automation system.
To overcome the above mentioned problem, the hydraulic system may comprises an accumulator or the like to compensate for the pulsations in the hydraulic head caused by known motion conversion devices. However, the use of such additional devices are not the ideal solution because they add to the complexity of the structure, making the control mechanism and routine maintenance unnecessarily complicated and burdensome.
It is, therefore, desirable to construct a rotary motion/constant velocity linear reciprocating motion conversion device which can convert rotary motion into constant velocity linear motion or vice versa, and a hydraulic system which can minimize a ripple associated with using the above-mentioned conversion device.